1. Field of the Invention
The present invention relates to means for modulating a carrier and in particular to means for generating a modulated wave having a uniform distribution of power among the carrier and a prescribed number of central sideband pairs.
2. Description of the Prior Art
The nonlinear characteristics of amplifiers of the class C and traveling wave tube (TWT) type, and the attendant intermodulation distortion induced in multicarrier signals when processed thereby is recognized and well documented. See, for example, G. Berretta, R. A. Gaugh and J. Guijarro, "Predicting Amplifier Performance of Multicarriers" Microwave Journal (July 1975) at pg. 35. The origin of such multicarrier distortion lies in the fact that the multiple equal power carriers have arbitrary phase relationships. Such carriers interact to produce a resultant signal exhibiting a large amount of amplitude modulation (AM). This inherent envelope (AM) time domain ripple is undesirable since the amplification processes within the above-named amplifiers convert the AM to phase modulation which results in serious distortion of the amplified signal. The weight reduction and efficiency achieved by the use of nonlinear saturated amplifiers, as opposed, for instance, to the linear class A amplifier is significant and extremely desirable for many applications. Thus the generation of pure frequency or phase modulated multiple equal line spectra represents a considerable advance in terms of the utility of saturated amplifiers by extending their light weight, efficient operation to applications requiring multiple equal-line spectra.
It has been shown in the past that a pure FM signal may be generated having a carrier and first sideband pair of equal power. However, attempts to extend this concept have incurred the significant spectral intermodulation effects described supra. Thus the achievement of distortionless, efficient amplification of the multi-carrier equal power signal has been limited to the case of just three equal amplitude spectra, those of a carrier and first sideband pair.